Women today get the majority of college degrees in America. It doesn’t matter what kind — associate’s, bachelor’s, master’s, or doctoral — women beat men in all the categories. In the 2009-2010 academic year, women earned 57.4 percent of all bachelor’s degrees.

Several theories have been put forth to explain this disparity, which is not by any means unique to the United States. One leading hypothesis is that boys simply chafe more within the boundaries of the classroom. In the U.S., high school boys are more likely to get in trouble than girls, and they have higher rates of arrest and suspension. They also report spending less time on homework.

That’s from a discussion in a 2006 paper on the college gender gap by economists Claudia Goldin, Lawrence Katz and Ilyana Kuziemko. “A more level and wider playing field for girls enabled them to blossom,” they write. “At the same time, the slower social development and more serious behavioral problems of boys remained and allowed girls to leapfrog over boys in the race to college.”

In other words: As things got more equal for boys and girls, a natural advantage began to reveal itself.

Recently, Elisa Olivieri, a PhD candidate at the University of Chicago, put forth a different explanation for why women are so much better at graduating college. Perhaps, she says, it has to do with the different kinds of careers that men and women want.

In the past 50 years, women began to work jobs traditionally held by college-educated men. They became doctors, lawyers, managers, engineers, and scientists. Of all white women who were either employed or stayed at home, the number who worked in male-dominated occupations was around 8 percent in 1960. That number was 29 percent by 2010. (Olivieri focuses on white women because historical changes in segregation make it harder to analyze trends among black women, though the results should be similar.)

Men, in contrast, have been much less willing to take positions traditionally held by college-educated women. More than three-quarters of public school teachers were women in 2008. And and more than 90 percent of nurses were women in 2011.

“Men have been so sluggish at entering these historically female college jobs,” Olivieri says. “At the same time, women were making advances into male fields, while still flowing into jobs like nursing and teaching.”

Olivieri argues that, in this way, sexism has been holding men back from college. By ceding to women careers like teaching and nursing, which require college degrees, men are more likely instead to work in jobs that don’t call for a diploma.

Is this an economically rational choice? Probably not. In her paper, which relies on Census data, Olivieri accounts for the disparities in wages between men and women working in the same occupation; disparities in how much manual labor different jobs require; and possible differences in each gender’s aptitude for college. Even after all these adjustments, she still finds there are certain jobs men just don’t want to do. It’s not really about the money; it’s about notions of masculinity.

Rather than working as teachers or nurses, it seems many men would prefer to take jobs in construction or manufacturing. This helps explain why women outnumber men in the lecture hall, Olivieri argues. Electricians don’t need to go to college; schoolteachers do. Her theory doesn’t rule out the possibility that women are simply better at college. But perhaps women are also more motivated than men because the jobs they want are more likely to require a degree.

In a 2010 article for The Atlantic, Hanna Rosin pointed out that more women than men were graduating from college, and also that traditionally female jobs were on the rise. She wondered, famously, if these twin trends spelled disaster for men. “What if the modern, postindustrial economy is simply more congenial to women than to men?” she wrote in the story, which later became a book called “The End of Men.”

By Olivieri’s calculations, the biggest obstacle keeping men out of college might be their own squeamishness about certain gendered jobs. They may have to change their minds soon. The returns from a bachelor’s degree are on the rise. And while traditionally male jobs like manufacturing have been disappearing, traditionally female jobs like nursing are in high demand.

That’s one reason we might see the college gender gap narrow in the coming years: Men just can’t afford to be sexist anymore.